Russia said it would target US aircraft after a Navy fighter jet downed a Syrian air force plane that dropped bombs near militia fighters aligned with the United States, according to reports.

“Any aircraft, including the international coalition’s planes and drones, discovered west of the river Euphrates, will be accompanied by ground and air-based anti-aircraft defenses as aerial targets,” Moscow said in a statement Monday.

The US said it acted in “collective self-defense” when an F-18 Super Hornet on Sunday shot down a Syrian SU-22 that had attacked a site near Tabqa occupied by members of the Syrian Democratic Forces.